Oxides, particularly iron oxides, supported on inert particulate matter have long been used in flow-through packed-bed processes to react with and scavenge hydrogen sulfide and thiols (mercaptans) present in natural gases and liquid hydrocarbons. The reactions between oxides and sulfides traditionally have been relatively slow, as compared to other sulfur removal or gas sweetening systems. Because of the slow rate of reaction, large iron oxide beds contained in large reactor vessels have been required in order to adequately remove hydrogen sulfide and thiols from the hydrocarbon fluids. The larger reaction vessels allow for longer contact times between the oxides and the sulfur compounds, with the longer contact times being necessary to adequately remove the sulfur compounds. A somewhat offsetting advantage to the slowness and size requirements of the iron oxide beds is that the reacted iron oxide bed material may be disposed of as non-toxic waste, unlike some other sulfur removal processes which require toxic waste disposal systems.
Current iron oxide based products designed to remove sulfur compounds from gas or vapor streams have performance limitations. An example of such a performance limitation relates to the minimum hydrocarbon fluid or gas residence time in a reactor vessel, as the residence time required for the gas in the vessel limits the space and practical vessel size in some cases. Minimum gas exposure or retention time in low pressure iron oxide beds typically ranges between about 1 to about 1.3 minutes based on the amount of unoccupied bed space and actual gas volume. Thus, large diameter vessels and beds are typically required for efficient design common in low pressure iron oxide bed applications. Large diameter vessels are also required in high pressure oxide processes, and, like low pressure iron oxide beds, are very expensive. Because of the lengthy gas retention time, it is difficult to fit vessel sizes into small foot print applications like offshore drilling or limited space plant facilities. Consequently, a problem exists because small vessel sizes cannot be used to sweeten hydrocarbon fluids, meaning certain facilities do not have access to packed bed iron oxide processes. Because of the space limitation, it would be desirable to have an iron oxide bed that required less space, preferably about half of the cross sectional area normally required, and was still capable of sweetening hydrocarbon fluids.
Unplanned increases in gas volumes and inlet hydrogen sulfide levels, beyond the design capacity of normal iron oxide beds, cause under-utilization of the iron oxide product and excessive costs. Iron oxide systems that are properly designed initially can experience increased gas flow and/or higher levels of hydrogen sulfide that significantly exceed normal design conditions resulting in inefficient utilization of iron oxide type products and substantially higher operating costs. Because unplanned increases in volume frequently occur, it is desirable to have a product and process that can handle increases in volume without wasting the iron oxide product.
An additional problem involves hydrocarbon fluids, gas and liquid, that are less than totally water saturated, as the unsaturated hydrocarbon fluids require long contact times to effectively remove hydrogen sulfide. Also, systems designed for water saturated conditions operate inefficiently when the fluid is not water saturated. Natural gas and vapor, and liquid hydrocarbon streams that are less than totally water saturated will result in the decreased removal efficiency of hydrogen sulfide by the iron oxide product and higher operating costs. Thus, a problem exists because current iron oxide products are commercially efficient only in the removal of dissolved hydrogen sulfide or other sulfur compounds in hydrocarbon fluids if there is sufficient contact time and the hydrocarbon fluids are saturated. Often, however, it is not practical to inject water to fully saturate the hydrocarbon fluid to achieve normal hydrogen sulfide removal. Consequently, it is desirable to have a system for sweetening hydrocarbon fluids that does not require the hydrocarbon fluids to be totally water saturated.
Systems designed to control odors in vapors from wastewater and oil tanker vent scrubber systems often utilize blowers and pressure boosters that create unsaturated gas or vapor streams by changing the physical properties of the hydrocarbon fluids. These operational practices can reduce the efficiency of iron oxide products in removing hydrogen sulfide and other sulfur compounds from fluids. Thus, it is desirable to have a system that can remove hydrogen sulfide and other sulfur compounds from gas and vapor streams that have constantly changing physical properties.
Additionally, some systems may inject air into the hydrocarbon fluid. The injection of air, which includes oxygen, causes increased corrosion and safety concerns despite increased capacity for hydrogen sulfide removal. The intentional and unintentional inclusion of air, including oxygen, in natural gas or vapor streams has long been seen to increase the capacity of iron oxide impregnated wood chips and other oxide products to react with hydrogen sulfide. However, corrosion and safety concerns are greatly increased due to the presence of oxygen, which will react with the vessel containing the oxide product. Also, many natural gas contracts presently specifically limit the amount of oxygen in the gas and some contracts prohibit the intentional injection of air due to problems caused downstream in gas transportation systems. The inclusion of a “non-oxidizer” stimulant or activator in the iron oxide product that enhances the capacity of sulfur removal, without the associated problems of organic and inorganic oxidizers, like air, would enhance the use of oxide products in sulfur removal processes.
Liquid hydrocarbons commonly include dissolved hydrogen sulfide and other sulfur compounds. In some cases, the hydrogen sulfide removal sufficiently meets the required product quality for sales to pipelines and transporters. Frequently, however, other sulfur compounds, such as mercaptans, carbonyl sulfides, and carbon disulfide need to be removed to meet required sulfur limits and product quality tests before the hydrocarbons can be sold. An improved iron oxide product that would efficiently remove hydrogen sulfide and other sulfur compounds to meet required sulfur limitations in hydrocarbon fluids would significantly increase the commercial utility of iron oxide sulfur removal processes.
Thus, it is desirable to have an iron oxide bed process and composition that functions in a small reactor vessel, removes sulfur compounds in a short amount of time, removes sulfur compounds from unsaturated fluids, does not require the injection of air, and removes most if not all of the sulfur compounds in a fluid, particularly a hydrocarbon fluid. As will be seen, the present invention activates the oxide bed process and composition to meet the above listed criteria.